1. Field of Invention
This invention relates generally to an air cleaning or filtering device which utilizes a cleanable or replaceable filter cartridge, and more particularly to a portable air cleaning or filtering device that includes a multipositional filter change indicator for indicating when to clean or replace the filter cartridge.
2. Background of Invention
Many air cleaning devices employ replaceable filters formed of an absorbent material arranged to establish a circuitous air flow path produced by an electrically powered blower. During normal operation of such air cleaning devices, the filters progressively accumulate particles that reduce the filter's permeability. Eventually, particulate accumulation in the filter diminishes the air flow through the air cleaning device significantly reducing its efficiency. At that time, the filter must be replaced to restore efficient air cleaning.
To assist a user in maintaining an efficient air cleaning operation, some air cleaning devices are equipped with indicators for monitoring the condition of a filter and indicating when it should be replaced. One such indicator comprises a transparent, vertically disposed tube having a lower end at atmospheric pressure and an upper end communicating with an internal portion of the air cleaner downstream from the filter. As the filter becomes clogged with particulate matter, an increased pressure drop occurs across the filter and a negative pressure is produced downstream thereof. As a result, a differential pressure occurs across the indicator tube and creates a force within the tubulation that lifts a visible indicator into a viewing window to provide an indication of a dirty filter.
Generally, the filter change indicator operates in one position, for example, with the air cleaning device oriented in either the upright or sideways position. Often the air cleaning device itself is operable in various positions, but the filter indicator becomes inoperative when the air cleaning device is placed in an orientation other than the indicator's intended operating position. The present invention overcomes the limitations of the prior art by providing a filter change indicator which is operable in various orientations of the device incorporating it.